Structural carbonaceous materials having improved surface erosion characteristics

ABSTRACT

Structural carbonaceous materials, such as graphite, having improved resistance to oxidation and corrosion at elevated temperatures are obtained by impregnating a solid carbonaceous material with a high boiling point hydrocarbon resin which leaves little or no residue on volatilization, such as a polyphenyl resin.

fiib? Vlllllfl uouwuu a lvvlll Rose et al. 51 Feb. 1, 1972 [54] STRUCTURAL CARBONACEOUS .[56] References Cited MATERIALS HAVING IMPROVED SURFACE EROSION UNITED STATES PATENTS CHARACTERISTICS 3,022,190 2/1962 Feldman.... ...102/1os x C 1 3,049,448 8/1962 Millet ..1 17/228 [72] Inventors: Emery T. Rose; Larry V. Pezzanlte, both 3,159,012 12/1964 Brunncr ..60/200 X of Lawrenceburg, Tenn. C [73] Assignee: Unlon Carblde Corporation 'T' Martin Assistant Examiner-D. Cohen |22] filed: Attorney-Paul A. Rose, Robert C. Cummings and John S. 211 Appl. No.: 679,567 Plscltelb [57] ABSTRACT [52] U.S.Cl ..ll7/l6l,239/265.l5, 102/105,

60/200 Structural carbonaceous materials, such as graphite, having [51] lnt.Cl ..F02k 1/24, F021: l1/02,B44d 1/09 improved resistance to oxidation and corrosion at elevated [58] Field of Search ..ll7/ 161 Ul-l, 228, DIG. 11; temperatures are obtained by impregnating a solid carbonaceous material with a high boiling point hydrocarbon resin which leaves little or no residue on volatilization, such as a polyphenyl resin.

8 Claims, No Drawings STRUCTURAL CARBONACEOUS MATERIALS HAVING IMPROVED SURFACE EROSION-CHARACTERISTICS BACKGROUND OF THE INVENTION materials are employed as facings for rocket nozzles, oxidationand chemical attack by the rocket fuel exhaust gases which pass over it causes an attrition of particles and gradual wearing away of the surface of such materials at temperatures above about 400500 C. This in turn alters the flow characteristics of the exhaust gases, thereby producing undesirable thrust vectors that reduce the stability of the missile.-

SUMMARY OF THE INVENTION In accordance with the instant invention, structural carbonaceous materials having improved resistance to oxidation and corrosion at elevated temperatures are obtained by impregnating a solid carbonaceous material with a high-boilingpoint hydrocarbon resin which leaves little or no residue on volatilization. Rocket nozzles prepared from graphite treated in this manner have been found to have a useful life of more than twice that of unimpregnated graphite. Although the exact manner in which these high-boiling resins provide protection against oxidation and corrosion is not fully understood, it is preferred, other hydrocarbon resins can be employed, including polyolefins such as polyethylene, polypropylene and polybutylene. Such resins are readily available commercially.

lnipregnationof the solid carbonaceous material according to the instant invention can be effected by any suitable .method. of effectively introducing the impregnant into the pores of said materialrThus'impregnation can be effected by :simply soading the material 'to be impregnated in the impregnant'while-maintaining the impregnant at a temperature above its melting point, orby using conventional methods of vacuum-pressure cycles to accomplish the same result.- In either event, the processshould be continued until from about 5 partsby volume to-about SOparts by'volume, preferably from about parts byvolume to about 40parts by volume, of

the impregnant'has been absorbed per l00parts by volume of the carbonaceous material, depending upon the density of the substrate and the impregnantpThe carbonaceous material may be.machined to its desired form either prior-to or after impregnation. In order to afford easier impregnant access to the surface to be protected, it is preferred to machine the mate rial so thatthe layerplanes of the surface to be exposed to the hot gas are perpendicular to the gas flow.

The following example is'set forth for purposes of illustration so thatthose skilled in the art may better understand this invention, and itshould be understood that it is not to be construed as limiting the invention in any manner.

EXAMPLE I Q Two l-inch X 1-inch X la-inch pieces of graphite were cut from adjacent areas of a slab 4-inch X6 inch X 5% inch. The

. graphite had an effective porosity of 30 percent.

believed that these resins, exude and volatilize at high temperatures and thereby provide a protective gas film over the surface of the nozzle substrate. Thus, at the onset of hot exhaust gas in the nozzle, the impregnant at the nozzle's surface becomes molten and begins to vaporize, thus forming a protective gas film at the exhaust gas-nozzle interface which immediately reacts to produce CO, CO, and other gases. The impregnani continues to volatilize at the surface, and as the exhaust gas reacts and removes impregnant from the'nozzle surface, additional impregnant is aspirated to the surface of the nozzle. The exudation and volatilizing of the resin serves to cool the substrate, and the protective film which forms reacts with the corrosive materials in the'exhaust gas stream and reduces the surface available for attack.

DESCRIPTION OF THE PREFERRED EMBODIMENT The corrosion and oxidation resistance of any structural carbonaceous material can be improved by impregnation with a high-boiling hydrocarbon in accordance with the instant invention provided it is porous enough to permit access of the im pregnant to the surface of the body. Preferably such material has a porosity of from about 5 percent to about'50 percent, most preferably from about 10 percent to about 40 percent. Below about 5 percent porosity, the capacity of the impregnant to penetrate the material is too low, while above about 50 percent porosity, the material loses the strength required to resist shear stresses applied to the nozzle by the exhaust gas. The term "carbonaceous as used throughout this specification is intended to include all forms of the material, both graphitic and nongraphitic forms.

ployed to impregnate structural carbonaceous materials according to the instant invention. While polyphenyls are One of the graphite pieces was placed in a vacuum chamber which was then evacuated to a pressure of 0.5 p.s.i.g. A solid polyphenylresin having a softening point of l35l45 C. and a boiling point of 500 C. (Montar 9) was then heated to 200 C. to liquefy it, and the liquefied resin was introduced into the chamber at a level about 1 inch above the graphite piece. After 30 minutes had elapsed, a pressure of p.s.i.g. was appliedand held for 1 hour. The weight increase of the graphite as a result of this treatment was 29 percent.

Theimpregnated graphite sample was then subjected to an oxyacetylene flame together with the unimpregnated graphite ,samplefor 30 seconds. The weight loss for the unimpregnated piece was 2.68 percent while the weight loss for the impregnated sample was only 0.20 percent (based on the original sample weight before impregnation).

What is claimed is:

1. A structural carbonaceous material impregnated with a normally solid polyphenyl resin having a boiling point of from about 200 C. to about 600 C. and which volatilizes to produce a vapor without leaving a residue, said carbonaceous material containing from about 5 parts by volume to about 50 parts by volume of the impregnant per 100 parts by volume thereof and having a porosity of from about 5 percent to about 50 percent prior to impregnation. I

2. An impregnated structural carbonaceous material as in claim l'wherein said carbonaceous material is graphite.

3. An impregnated structural carbonaceous material as in claim Zin the shape of a rocket nozzle 4. An impregnated stiu'c t ural carbonaceous material as in claim 3 wherein the layer planes of the surface to be exposed to the exhaust gas are perpendicular to the gas flow.

5. A structural carbonaceous material as in claim 1 wherein the polyphenyl resin has a boiling point of from about 250 C.

7 cent priorto impregnation.

6. Animpregnated structural carbonaceous material as in claim 5 wherein said carbonaceous material is graphite.

7 An impregnated structural carbonaceous material as in claim 6 in the shape of a rocket nozzle.

8. An impregnated structural carbonaceous material as in claim 7 wherein the layer planes of the surface to be exposed to the exhaust gas are perpendicular to the gas flow. 

2. An impregnated structural carbonaceous material as in claim 1 wherein said carbonaceous material is graphite.
 3. An impregnated structural carbonaceous material as in claim 2 in the shape of a rocket nozzle.
 4. An impregnated structural carbonaceous material as in claim 3 wherein the layer planes of the surface to be exposed to the exhaust gas are perpendicular to the gas flow.
 5. A structural carbonaceous material as in claim 1 wherein the polyphenyl resin has a boiling point of from about 250* C. to about 550* C. and wherein said carbonaceous material contains from about 10 parts by volume to about 40 parts by volume of the impregnant per 100 parts by volume thereof and has a porosity of from about 10 percent to about 40 percent prior to impregnation.
 6. An impregnated structural carbonaceous material as in claim 5 wherein said carbonaceous material is graphite.
 7. An impregnated structural carbonaceous material as in claim 6 in the shape of a rocket nozzle.
 8. An impregnated structural carbonaceous material as in claim 7 wherein the layer planes of the surface to be exposed to the exhaust gas are perpendicular to the gas flow. 